Full polymer microresonators

ABSTRACT

The present invention relates to a microresonator, in particular a full polymer microresonator, a method for producing the microresonator, and the use of the microresonator as a microlaser and/or molecular sensor.

This application claims priority to German patent Appl. no. 10 2014 012981.0, filed Sep. 2, 2014, which is incorporated by reference in itsentirety.

FIELD

The present invention relates to a microresonator, in particular a fullpolymer microresonator, a method for the production of themicroresonator, and the use of the microresonator as a microlaser and/ormolecular sensor.

BACKGROUND

Optical microresonators, using which light can be enclosed in anultra-small space for a long time, are known in the prior art. Thesemicroresonators can be used as microlasers, for example, in particularmicro-cup lasers, and are producible in large piece counts and highcomponent density on a chip basis. These structures can be used, interalia, for the employment as a laser light source in chip-based photonicsystems and as a central detection element in the meaning of abiosensor.

Conventional microresonators typically consist of a substrate, apedestal, and the actual resonator. The resonator, for example, in cupshape, is connected in this case via the pedestal to the substrate,which is typically a silicon wafer and is used as a carrier. Thepedestal always consists in this case of the same material as thesubstrate.

Micro-cup resonators are typically manufactured according to earlierdescriptions by a four-step production method. In the first step, asilicon wafer is coated with a polymer photoresist by means of spincoating, wherein the polymer photoresist forms the resonator material.In this polymer, disks having a diameter in the two-figure tothree-figure micrometer range are defined in the second step in themeaning of a positive photoresist by means of photolithographic.methods. After a suitable (wet) chemical development of the exposedregions, polymer disks on silicon are obtained. In the third step, thesedisks are isotropically undercut using xenon difluoride (XeF₂), so thatthe edge regions of the polymer disks are exposed and are connected viathe pedestal made of silicon to the silicon wafer. Since the edgeregions of the polymer disks are exposed, low-loss light guiding isenabled inside the disks. In the final, fourth process step, the entirestructure is heated above the glass transition temperature of thepolymer. A reduction of disadvantageous surface roughness in the polymeris achieved by this thermal reflow process. Furthermore, thecharacteristic cup shape of the cup resonators forms as a result of thereduction of the surface energy. The resonator surface is then generallyfree of defects and enables optical quality factors greater than 10⁷,which are typically limited by intrinsic properties of the polymer.

The preceding production method has disadvantages in particular withregard to the further use of the microresonators for biosensors,however. The use of XeF₂ restricts the production method of themicroresonators to silicon as the substrate material, whereby thepossible uses of the resonators as biosensors are substantiallyrestricted. In this area of application, for example, transparent (forexample, for microscopic applications) and/or mechanically flexiblesubstrate materials would be desirable. In addition, the XeF₂ etchingprocedure is a high-vacuum process, which is very time-consuming (infeedand outfeed of the chips, generation of a stable vacuum, etc.) andadditionally presumes a costly infrastructure. In addition, even largeXeF₂ etching facilities are very restricted in their throughput, sincethe substrates to be etched cannot exceed a specific maximum size.

XeF₂ itself is a very costly and highly corrosive chemical. If theoptimum vacuum parameters are not precisely maintained during theetching procedure or if atmospheric contaminants and/or residualmoisture are present in the etching chamber, interfering organicreaction byproducts form on the resonator surface during the etchingprocedure. These are disadvantageous in the further use of themicroresonators since, for example, subsequent immobilization of theacceptor molecules, which are absolutely required for biosensors, on theresonator surface can no longer be reproducibly applied. Such changesmay be directly detected, for example, by way of a change of the watercontact angle on the polymer surface.

The etching using XeF₂ is therefore not feasible for mass production,which is efficient in time and costs and is reproducible. However, theundercutting of the disks is absolutely necessary for the production ofthe resonators, since the functionality of the component as an opticalelement is first enabled in this way. In addition, it is a furtherdisadvantage that it was previously not possible by way of the XeF₂etching procedure to set the pedestal height independently of thepedestal diameter or to create vertical sequences of pedestals andresonators.

SUMMARY

The present invention is therefore based on the object of providing amicroresonator, which may be produced via a method without XeF₂ etchingprocedure and is therefore not restricted to silicon in the selection ofthe substrate material, and also a method for producing thismicroresonator.

This object is achieved by the embodiments of the present inventioncharacterized in the claims.

In particular, a microresonator is provided according to the invention,comprising, in this sequence, a substrate, an intermediate layer as apedestal, and a resonator, wherein the intermediate layer comprises anorganic or inorganic polymer.

By providing the specific intermediate layer between resonator andsubstrate material, it is advantageously possible to provide themicroresonator according to the invention without an XeF₂ etchingprocedure. By avoiding this etching procedure, it is advantageouslypossible to also use other materials in addition to silicon, forexample, transparent and/or mechanically flexible materials, as thesubstrate material for the microresonator according to the invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the sequence of the individual method stepsin the method according to the invention for producing a microresonator.I. Spin coating of the intermediate layer material; IIa. Spin coating ofthe resonator material or IIb. Stamp coating; IIIa. Structuring via UVor electron-beam writer or IIIb. Stamp transfer; IVa. Developing theresonator material or IVb. Stamp separation; V. Selectivedissolving/etching out of the intermediate layer material; VI. Thermaltreatment. Reference numerals 1 refers to an intermediate layermaterial; 2 refers to a substrate; 3 refers to a stamp; 4 refers to aresonator material; and 5 refers to an isotropically undercut pedestalbetween resonator and substrate.

FIG. 2 schematically shows the sequence of the individual method stepsin the method according to the invention for producing a sequence ofmicroresonators having vertically stacked layers. I. Spin coating of theintermediate layer material; II. Spin coating of the resonator material;III. Repeated spin coating of intermediate layer material and resonatormaterial; IV. Structuring via UV or electron-beam writer; V. Selectivedissolving/etching out of the intermediate layer material. Referencenumerals 1 refers to an intermediate layer material; 2 refers to asubstrate; 3 refers to a stamp; 4 refers to a resonator material; 5refers to an isotropically undercut pedestal between resonator andsubstrate; and 6 refers to an isotropically etched pedestal between twolight-guiding layers.

FIG. 3 shows a scanning electron microscope picture of an array made ofthree micro-cup resonators according to the invention.

FIG. 4 shows the laser characteristic curve of a pigment-doped micro-cuplaser according to the invention on a pedestal made of polymer.

FIG. 5 shows a light microscope picture of a micro-cup laser accordingto the invention during the optical excitation by means of pump laser.

The present invention will be explained in greater detail on the basisof the following, nonrestrictive examples.

DETAILED DESCRIPTION

According to the invention, the term “microresonator” is understood as ageometric arrangement in a size range of less than 1 mm, whichcomprises, in this sequence, a substrate, an intermediate layer as apedestal, and a resonator. The shape of the resonator is not subject toany special restriction according to the invention. The resonator has,for example, the shape of a cup, a disk (cylinder), a toroid, a sphere,etc., as are known to a person skilled in the art as possible resonatorshapes. According to one preferred embodiment, the resonator is in cupshape.

In the microresonator according to the invention, the intermediate layeras the pedestal connects the substrate to the resonator. Theintermediate layer comprises an organic or inorganic polymer, which canbe isotropically dissolved/etched out by wet chemistry selectively inrelation to the other layers, i.e., the substrate and the resonator.According to the invention, the term “polymer” is understood as anyorganic or inorganic polymer and copolymer and also mixtures of polymersand/or copolymers. Inorganic polymers are, for example, polysilanes,polysiloxanes, polytitanates, polygermanates, polyzirconates,polysulfazenes, polyphosphates, polyphosphazenes, polyboronitrides, etc.

According to one embodiment, the intermediate layer comprises furtheradditives, which can cause increased stability of the layer or furtherfunctionalities, for example. Thus, for example, by adding magneticallyor electrically conductive particles to the intermediate layer material(pedestal material), the resonator can be electrically contacted andcharged particles can be conducted to the resonator by the resultingmagnetic field or electrical field. If a polymer or copolymer havingfunctional chemical end groups is used as the intermediate layermaterial, the pedestal surface can thus advantageously be passivated ina targeted manner, so that molecules can exclusively accumulate on theresonator itself.

The intermediate layer additionally can preferably be processed out of asolution and is compatible in production with the resonator material.This means that the intermediate layer is insensitive in relation toboth the solvent and the developer of the resonator material. Inaddition, the resonator material must adhere sufficiently to theintermediate layer and no disadvantageous chemical reaction can takeplace between the layers, in particular not even during heating of theentire structure above the glass transition temperature of the resonatormaterial. The intermediate layer preferably has a higher glasstransition temperature than the resonator material, since in this waywarping or collapsing of the structure of the microresonator accordingto the invention during heating can be avoided. According to oneparticularly preferred embodiment, the intermediate layer has a glasstransition temperature which is at least 30° C. higher than theresonator material.

According to one preferred embodiment of the present invention, thepolymer of the intermediate layer comprises an organic polymer.According to one particularly preferred embodiment of the presentinvention, the polymer of the intermediate layer ispolydimethylglutarimide.

The thickness of the intermediate layer is not subject to any specialrestriction according to the invention. According to one preferredembodiment, the intermediate layer has a thickness of 1 μm to 1 mm,particularly preferably of 5 μm to 25 μm. In the case of intermediatelayer thicknesses less than 1 μm, the distance between the substrate andthe light-guiding edge of the resonator becomes so small that undesiredcoupling of the light out of the resonator into the substrate can occur,whereby the resonator quality can worsen. The diameter of the pedestalis preferably 10% to 80% of the resonator diameter, particularlypreferably 33% to 66%, since an ideal cup shape with good stability atthe same time is achieved in these ranges in particular in the case ofcup-shaped resonators.

In the microresonator according to the invention, the substrate is usedas a carrier of the intermediate layer (pedestal layer), on which theresonator is in turn located. The substrate is not subject to anyspecial restriction according to the invention. Since the pedestal inthe microresonator according to the invention does not consist ofsilicon as in the prior art, but rather comprises an organic orinorganic polymer, in the production method of the microresonatoraccording to the invention, the substrate material is advantageously notrestricted to silicon, but rather the substrate material can be freelyselected, whereby it can have particularly favorable properties withrespect to the respective application of the microresonator.

A biocompatible substrate and/or (mechanically) flexible films, whichare inexpensive in comparison to silicon wafers, and which can be cutand separated without particle contamination, can advantageously be usedas the substrate material. According to the invention, the term“biocompatible” means that components in an analyte, for example,biomolecules, do not degrade upon contact with the substrate, i.e.,change their shape and/or functionality, and therefore no longer can bebound by the biofunctionalization of the resonator surface.Biocompatible polymer substrates are, for example, polymethylmethacrylate, polysulfone, cyclo-olefin copolymer, etc. Furthermore,transparent substrates are advantageously possible, which enable opticaladdressing and readout of the resonator structure through the substrate,as well as already pre-structured substrates. According to theinvention, the term “pre-structured substrates” is understood to meansubstrates which were already pre-structured in preceding process steps(for example, by means of milling, drilling, photolithography, etching,impression, or vapor deposition) and have a surface topography. Sincethe substrate itself is not ablated during the etching of the pedestaldue to the intermediate layer, a previously produced electrical,micromechanical, microfluidic, or microoptical structure can also beprovided on the substrate. The resonators may thus be produced, forexample, on microelectronic chips, on microoptical lenses, or inmicrofluidic channels.

According to one embodiment, the substrate comprises cyclo-olefincopolymers and/or polysulfone. Furthermore, all transparent materials(transparent polymers, glasses, etc.) are advantageous, since they aretransparent to excitation and emission light, and (mechanically)flexible materials (for example, polymer films), since the substrate canthen be deformed or adapted to any arbitrary surface shape (for example,introduction into microfluidic structures, cannulas, application toother geometries, etc.). Depending on the application, however, metalfoils can also be advantageous for applications. “Functional” substratesare particularly advantageous, the optical or mechanical properties ofwhich may be intentionally varied during operation, for example, shapememory materials, the shape of which may be intentionally varied via thetemperature, for example. If at least two resonators are structured at asmall distance on a shape memory material, the distance between them maybe set in a controlled manner, so that optical coupling can beimplemented. The coupling properties may be intentionally modified viathe distance of the structures.

The thickness of the substrate is not subject to any special restrictionaccording to the invention. The substrate is used as a carrier of theresonators and must therefore ensure the required stability orflexibility. This is dependent on the material and application.According to one preferred embodiment, the substrate has a thickness of1 μm to 5 mm, particularly preferably 50 μm to 1 mm. For the polymersubstrates used, the minimum thickness is to be 50 to 100 μm, forexample, since the films could otherwise tear. However, the substratebecomes heavier and more expensive with increasing thickness and, in thecase of transparent substrates, the absorption additionally rises.Therefore, the above maximum substrate thickness is not to be exceeded.

The resonator of the microresonator according to the invention is notsubject to any special restriction and any material which is known to aperson skilled in the art as a suitable material for the production of aresonator of micro-cup resonators can be used as the resonator material.The resonator can have any arbitrary shape (for example, cup, disk,sphere, toroid). Suitable materials are transparent in the spectralrange used, have low optical damping, and have an index of refractionwhich is greater than that of the ambient medium, to fulfill therequirement for total reflection. Possible materials are, for example,photoresists such as SU-8, ormocere, and/or PMMA-based copolymers.According to one preferred embodiment of the present invention, thematerial from which the resonator is formed (“resonator material”)comprises a polymer or a copolymer. If a polymer or copolymer is used asthe resonator material, an expanded functionality can advantageously beintroduced into the polymer matrix, for example, in the form of dopingwith a laser pigment. According to one particularly preferredembodiment, the resonator material comprises polymethyl methacrylate(PMMA), optionally as a copolymer having a 5 to 10 wt.-% fraction of,for example, methacrylic acid or polyglycidyl methacrylate. PMMAadvantageously offers, in addition to very good optical properties, lowmaterial costs and can be processed at comparatively low temperatures byway of process steps suitable for mass production. In addition, PMMA canbe structured on a nanometer scale and can be processed usingconventional hot stamping methods.

According to one preferred embodiment of the present invention, thematerials of the intermediate layer and the resonator are different fromone another, so that in the production method of the microresonatoraccording to the invention, a thermal reflow step is possible as anoptional last production step, by which surface defects can be reduced.Resonators having particularly high quality factors may thusadvantageously be provided, which can be used in particular inbiosensors. If a microresonator is provided, the substrate, intermediatelayer, and resonator of which are exclusively formed from polymers andcopolymers, this is referred to as a full polymer microresonator.

The thickness of the resonator, i.e., the spatial extension of theresonator from the lower side thereof, which comes into contact with theintermediate layer, up to the upper side of the resonator, is notsubject to any special restriction according to the invention. Accordingto one preferred embodiment, the resonator has a thickness of 100 nm to5 μm, particularly preferably 800 nm to 2 μm. In the case of resonatorshaving a thickness of less than 100 nm, the hazard exists that theresonators will collapse during the undercutting or during thesubsequent reflow.

The diameter of the resonator is not subject to any special restrictionaccording to the invention. For example, the resonator has a diameter of5 μm to 1 mm, preferably 20 μm to 100 μm.

According to one embodiment of the present invention, the microresonatorhas two or more intermediate layers and two or more resonators, whereinthe intermediate layers and resonators are arranged alternately one ontop of another, i.e., a vertically stacked sequence of resonators andintermediate layers (intermediate pedestals) is provided. The number ofthese layer pairs can be from 2 to 10, for example. The above embodimentcan thus have vertically coupling resonator structures, whichadvantageously enable the creation of high-sensitivity biosensors orlasers having a single emission wavelength by way of the Vernier effect.Due to a freely selectable sequence of different polymers or copolymersin such a structure as the light-guiding layers (resonators), which canhave different functionalizations in a biosensor experiment, a largenumber of sensor elements and reference elements may advantageously beimplemented extremely compactly and with high component density.

According to one embodiment of the present invention, multiplemicroresonators according to the invention are arranged on the substrateto form a (large-area) array.

A further aspect of the present invention relates to a method forproducing the microresonator according to the invention, comprising thefollowing steps:

-   (a) providing a substrate;-   (b) applying an intermediate layer material to the substrate,    wherein the intermediate layer material comprises an organic or    inorganic polymer;-   (c) applying a disk-shaped resonator to the intermediate layer    material; and-   (d) selectively dissolving/etching out the intermediate layer    material to form a pedestal and to obtain the microresonator.

All above embodiments relating to the microresonator according to theinvention also apply to the method according to the invention forproducing the microresonator.

In step (a) of the method according to the invention, a substrate isprovided, wherein the substrate can advantageously consist of anarbitrary material because of the following method steps. Thefabrication parameters of the following method steps are advantageouslyalso substrate-independent, so that adaptation of the production to agiven substrate material is omitted.

In step (b) of the method according to the invention, an intermediatelayer material is applied to the substrate, wherein the intermediatelayer material comprises an organic or inorganic polymer. Theintermediate layer material can be applied using any application methodknown to a person skilled in the art. The thickness of the intermediatelayer material, which then later corresponds to the thickness of theintermediate layer as the pedestal, can be freely selected in this caseand adapted to the desired later application. According to oneembodiment of the present invention, the intermediate layer material isapplied by means of spin coating.

In step (c) of the method according to the invention, a disk-shapedresonator is applied to the intermediate layer material. The resonatorcan be applied using any application method known to a person skilled inthe art.

According to one embodiment of the method according to the invention,step (c) comprises the following steps:

-   (c1) applying a resonator material to the intermediate layer    material;-   (c2) lithographic structuring of the applied resonator material in    disks; and-   (c3) developing the lithographically structured resonator material.

In step (c1), a resonator material is applied to the intermediate layermaterial. The resonator material can be applied using any applicationmethod known to a person skilled in the art. According to one embodimentof the present invention, the resonator material is applied in step (c1)by means of spin coating.

In step (c2), the applied resonator material is lithographicallystructured in disks. The resonator material can be structured using anylithographic method known to a person skilled in the art. According toone embodiment, the resonator material is structured by means ofelectron beam lithography. According to an alternative embodiment, theresonator material is structured by DUV lithography, whereby large piececounts of resonators may advantageously be manufactured in a parallelproduction method.

In step (c3), the lithographically structured resonator material isdeveloped. The development is performed in this case by methods known toa person skilled in the art, for example, by a wet-chemical processstep.

According to an alternative embodiment, step (c) comprises step (c4),stamp transfer of the resonator to the intermediate layer material. Inthis case, the resonator is applied by means of a stamp to theintermediate layer material already in disk form, so that a subsequentdeveloping step like above-described step (c3) can be omitted. Inparticular for industrial production of large piece counts, a stamptransfer method is very advantageous, since it enables very large-areaand cost-effective production. For the transfer, for example, a stamp isused, on the surface of which protrusions in the form of the resonatorsare applied. The surface energy of the stamp can be reduced by ananti-adhesive coating, for example, made of perfluorinated polymers suchas Teflon, so that the resonator material deposited thereon only adheresslightly to the stamp surface. If the stamp is brought into contact witha substrate having higher surface energy, the resonator material on theprotruding stamp surfaces is then transferred to the substrate.Disk-shaped resonators are thus advantageously obtained on the substratewithout lithographic structuring and development. The subsequentprocessing of the intermediate layer and optional reflow process canremain unchanged.

In step (d) of the method according to the invention, the intermediatelayer material is selectively dissolved/etched out to form a pedestal.This step is preferably performed as wet chemical isotropic etching,during which the resonator material is partially undercut, so that theremaining intermediate layer subsequently forms the pedestal betweensubstrate and resonator. The etching in step (d) is carried out suchthat at least the edge of the resonator disk is exposed, so that theoptical modes in the resonator which extend along the outer edge do notinteract with the pedestal and are not damped thereby. Step (d) is notsubject to any further restriction and the required method parameters(etching chemicals, etching duration, etc.) for wet chemical etching areknown to a person skilled in the art depending on the intermediate layermaterial used.

According to one embodiment, the method further comprises step (e),thermal treatment of the microresonator obtained in steps (a) to (d) toreduce surface defects. In addition, a micro-cup resonator with reducedsurface defects can be obtained according to one embodiment by optionalstep (e).

In optional step (e) of the method, the manufactured/resulting structurein steps (a) to (d) is thermally treated to achieve a reduction ofdisadvantageous surface roughness. Furthermore, according to oneembodiment of the present invention, the characteristic cup shape of theresonators forms as a result of the reduction of the surface energy.

According to one embodiment, the thermal treatment is carried out for aduration of 1 second to 1 hour, preferably 5 seconds to 1 minute. Withan excessively short duration, the risk exists that the time will not besufficient for uniform heating of the substrate and the reflow processwill not be started or will not be completely finished. With anexcessively long duration, the risk exists that potentially present,temperature-sensitive laser pigments in the resonator material and/orthe chemical end groups of optionally used functional copolymers forsurface functionalization can degrade. The thermal treatment ispreferably carried out at temperatures of 110° C. to 180° C.,particularly preferably 125 to 140° C. According to one preferredembodiment, the temperature is approximately 10 to 30° C. above theglass transition temperature of the resonator material. If PMMA is usedas the resonator material, for example (glass transition temperatureapproximately 110° C.), the reflow is thus preferably performed at 125to 140° C. For copolymers having a higher or lower glass transitiontemperature, the reflow temperature has to be increased or decreasedaccordingly. The reflow temperature should thus tend to be approximately10 to 30° C. above the glass transition temperature. According to theinvention, the above temperature for the thermal treatment is defined asthe temperature which the heating plate or the furnace has, on which/inwhich the substrate is heated.

FIG. 1 schematically shows the sequence of the individual method stepsin the method according to the invention for producing a microresonatoraccording to the invention, wherein the above-described variants of step(c) are shown (I. Spin coating of the intermediate layer material; IIa.Spin coating of the resonator material or IIb. Stamp coating; IIIa.Structuring via UV or electron-beam writer or IIIb. Stamp transfer; IVa.Developing the resonator material or IVb. Stamp separation; V. Selectivedissolving/etching out of the intermediate layer material; VI. Thermaltreatment).

According to one embodiment of the method according to the invention,steps (b) and (c) are carried out multiple times alternately insuccession. In this way, a sequence of microresonators canadvantageously be provided, which has two or more intermediate layersand two or more resonators. If step (c) of the method according to theinvention comprises steps (c1), (c2), and (c3), step (c3) is thuspreferably only carried out when all intermediate layers and resonatorlayers have been applied. FIG. 2 schematically shows the sequence of theindividual method steps in the method according to the invention forproducing a sequence of microresonators having vertically stacked layers(I. Spin coating of the intermediate layer material; II. Spin coating ofthe resonator material; III. Repeated spin coating of intermediate layermaterial and resonator material; IV. Structuring via UV or electron-beamwriter; V. Selective dissolving/etching out of the intermediate layermaterial).

The chemical functionality of the resonator surface can be reproduciblyensured by wet chemical step (d) of the method according to theinvention. This is absolutely necessary for a use of the microresonatorof the present invention as a biosensor, which presumes a subsequentchemical functionalization of the resonator surface. Furthermore,flexible and very well reproducible monitoring of the pedestal height orthe pedestal diameter is possible by way of the method according to theinvention, in particular since pedestal height and diameter are variablyadjustable independently of one another. Height and diameter of thepedestal can advantageously be adjusted by monitoring the appliedintermediate layer or the duration of the wet chemical undercutting.This is essential in particular for the integration of themicroresonator in a lab-on-a-chip environment and was not achievable bythe previously known method using XeF₂ etching procedure, in whichpedestal height and diameter are not variable independently of oneanother.

A further aspect of the present invention relates to the use of themicroresonator according to the invention or the microresonator or thearray made of microresonators according to the invention, which isproduced via the method according to the invention, as a microlaserand/or molecular sensor. Thus, the microresonator according to theinvention can be used, for example, in the analysis of blood serum orplasma, urine, saliva, and/or other bodily fluids for diagnosingillness. Because of its cost-effective mode of production, themicroresonator according to the invention is particularly suitable forthis purpose, since applications in biosensors preferably requireanalysis chips, which are to be used as disposable components because ofpossible contamination during the analysis or for hygienic reasons.

In the present invention, by introducing an intermediate layer as apedestal between resonator and substrate, an XeF₂ etching procedure isadvantageously omitted and for the first time the pedestal required forthe light-guiding resonator is implemented via a wet chemical method.The method according to the invention therefore represents, on the onehand, a significant simplification of the production process andadditionally also enables microresonators to be provided, in which thesubstrate material can be freely selected and individually adapted tothe respective desired application. It is thus advantageously possiblein the microresonator according to the invention to use, for example,transparent and/or mechanically flexible materials and/or pre-structuredsubstrates. In addition, vertically stacked resonator layers having avariable layer sequence in adjustable distances between the layers canadvantageously be provided, which may then have differentbiofunctionalizations in a layer-selective manner upon the use ofdifferent polymers and/or copolymers.

By avoiding the XeF₂ etching procedure, the method according to theinvention does not require any process steps in high vacuum, in contrastto the previously known methods. The simplification of the productionmethod which advantageously accompanies this results in independence ofthe method from any type of the substrate, the substrate size, and thesubstrate shape. In addition, the use and occurrence of highly toxicchemicals is avoided and the expenditure in time and apparatus for theproduction is significantly reduced.

The method according to the invention advantageously enables large-scaleindustrial production and, in particular if a flexible substratematerial is used, manufacturing of the structures using establishedprinting methods, for example, UV nanoimprinting, roll-to-rollproduction processes (UV assisted and non-UV assisted, vapor deposition,use of the roll as an impression tool, use of a second foil as animpression tool, etc.), stamp transfer techniques (for example,microcontact printing), and impression processes, for example, hotstamping, replica molding, microtransfer molding, capillarymicromolding, etc.

Because of the above advantages and special features of themicroresonator according to the invention and the method according tothe invention for producing these microresonators, the microresonatorsof the present invention are advantageously outstandingly usable inparticular for detecting ultrasmall virus and particle concentrationsdown to detecting individual molecules in a variety of applications inmedicine, pharmacology, biology, and chemistry.

Production Example 1

The commercially available polymer LOR 30B (Microchem) based onpolydimethylglutarimide was applied by means of spin coating as theintermediate layer material in a layer thickness of 5 μm onto a siliconwafer as the substrate. The structure was subsequently temperaturetreated for 5 to 30 minutes at 180° C. To prevent bubbling, thetemperature was continuously increased within 5 to 90 minutes from roomtemperature to 180° C. A 1.2 μm thick layer of PMMA 950k (Microchem) wasthen applied to the intermediate layer material by means of spin coatingas the resonator material and the structure was temperature treatedduring a heating duration of 5 minutes at 110° C. Electron beamlithography was used for the lithographic structuring of disks having 50μm diameter in the PMMA layer (resonator material). The exposed PMMA wasselectively developed using a mixture of methyl isobutylketone andisopropanol (mixture ratio 1:1). A developer based on tetramethylammonium hydroxide (101 A developer from Microchem) was used for theselective etching of the LOR layer (intermediate layer material). Theetching duration was set so that the PMMA disks were undercut by half,i.e., between 30 and 60 minutes. Subsequently, the structure obtainedwas heated on a heating plate for 30 seconds to 130° C. for the thermalreflow of the resonators. The cup shape of the resonators resulted inthis case.

FIG. 3 shows three micro-cup resonators produced in this manner. The cupshape is very homogeneous because of the thermal reflow process and thepedestal diameter of the micro-cup resonators is adjustable in acontrolled manner.

Production Examples 2 and 3

Micro-cup resonators were produced similarly to production example 1,wherein instead of the silicon wafer, polymer films having 200 to 350 μmthickness made of cyclo-olefin copolymer (COC; production example 2) andpolysulfone (PSU; production example 3) were used as the substrates.Except for a slight increase of the reflow temperature from 130° C. to135° C. because of the lower thermal conductivity of the substratematerials used, identical method parameters were used as in productionexample 1.

Micro-cup resonators were able to be produced successfully using bothsubstrate materials. This shows clearly that the production methodaccording to the invention is independent of the substrate materialused.

Production Example 4

To produce stacked resonators, the first two steps of production example1, i.e., the spin coating of LOR resist and PMMA, were repeated multipletimes in succession. Subsequently, the photosensitive resist was exposedin one step and the entire structure was created by a sequence ofdevelopment steps.

Test Example 1

The optical properties of the cup resonators were characterized at ameasuring station for laser characteristic curves. For this purpose, thelaser pigment pyrromethene 597 was admixed to the PMMA before theproduction of the micro-cup resonators, so that the cups function asmicrolasers.

FIGS. 4 and 5 show the laser characteristic curve of a resonator on apedestal (intermediate layer) made of liftoff resist 30B (Microchem),which is based on polydimethylglutarimide, and a light microscopepicture of the micro-cup laser during the optical excitation by means ofpump laser. The laser threshold is approximately 220 pJ per applicationpulse and is therefore in the same range as the laser threshold of cuplasers on a silicon pedestal. The production of micro-cup resonators onpolymer pedestals therefore does not influence the optical quality ofthe resonators.

Test Example 2

The cup lasers of production examples 2 and 3, which were produced onthe polymer substrates made of PSU and COC, could be optically pumpedand read out successively through the transparent substrate. Thisadvantageously enables the optical addressing to be performed at aseparate location from the fluidic addressing for applications inbiosensors. Thus, for example, the fluidic supply of the analyte can beperformed on the chip front side, while the optical addressing isperformed from the chip rear side.

1. A microresonator, comprising, in this sequence, a substrate, anintermediate layer as a pedestal, and a resonator, wherein theintermediate layer comprises an organic or inorganic polymer.
 2. Themicroresonator as claimed in claim 1, wherein the glass transitiontemperature of the polymer is greater than that of the material of theresonator.
 3. The microresonator as claimed in claim 1, wherein thepolymer is polydimethylglutarimide.
 4. The microresonator as claimed inclaim 1, wherein the intermediate layer has a thickness of 1 μm to 1 mm.5. The microresonator as claimed in claim 1, wherein the substrate istransparent and/or biocompatible and/or mechanically flexible.
 6. Themicroresonator as claimed in claim 1, wherein the substrate comprisescyclo-olefin copolymers and/or polysulfone and/or a glass.
 7. Themicroresonator as claimed in claim 1, wherein the microresonator has twoor more intermediate layers and two or more resonators, wherein theintermediate layers and resonators are arranged alternately one on topof another.
 8. A method for producing a microresonator as claimed inclaim 1, comprising the following steps: (a) providing a substrate; (b)applying an intermediate layer material to the substrate, wherein theintermediate layer material comprises an organic or inorganic polymer;(c) applying a disk-shaped resonator to the intermediate layer material;and (d) selectively dissolving and/or etching out the intermediate layermaterial to form a pedestal and to obtain the microresonator.
 9. Themethod as claimed in claim 8, further comprising step (e) of thermallytreating the microresonator obtained in steps (a) to (d) to reducesurface defects.
 10. The method as claimed in claim 8, wherein steps (b)and (c) are carried out multiple times alternately in succession. 11.The method as claimed in claim 8, wherein step (c) comprises thefollowing steps: (c1) applying a resonator material to the intermediatelayer material; (c2) lithographic structuring of the applied resonatormaterial in disks; and (c3) developing the lithographically structuredresonator material.
 12. The method as claimed in claim 8, wherein step(c) comprises the following step: (c4) stamp transfer of the resonatorto the intermediate layer material.
 13. A microlaser and/or molecularsensor comprising the microresonator of claim 1.